By Ronnel Alumia, BSN, RN, WCC, CWCN, OMS

Achieving excellent wound care outcomes can be challenging, given the growing number of high-risk patients admitted to healthcare facilities today. Many of these patients have comorbidities, such as obesity, diabetes, renal disease, smoking, chronic obstructive pulmonary disease, and poor nutritional status. These conditions reduce wound-healing ability.

At the same time patient acuity has been rising, reimbursement for some types of care has been declining. For certain hospital-acquired conditions, such as stage III or IV pressure ulcers and certain surgical-site infections, reimbursement has been eliminated. Thus, clinicians can’t choose products based solely on their proven ability to obtain a good clinical outcome; they also must consider economic factors. Noncontact low-frequency ultrasound (NLFU) can help improve clinical outcomes and provide cost savings.

Ultrasound: Simple but effective

NLFU delivers sound waves to tissues through a saline mist. Unlike most wound care treatments, whose effects are limited to the surface, NLFU penetrates into and below the wound bed to reach previously inaccessible tissues. (See A glimpse of NLFU in action by clicking the PDF icon above.)

View: See how NLFU works

Ultrasound energy produces biophysical effects from mechanical stimulation of cells, promoting wound healing. A mechanical vibration, ultrasound is transmitted at a frequency above the upper limit of human hearing—20 kHz. The most common form of therapeutic ultrasound uses devices that operate in the 1- to 3-MHz range to treat various musculoskeletal disorders with a thermal effect. Diagnostic ultrasound, in contrast, operates in a high-frequency (20 to 40 MHz) range. It has a wide number of uses, from fetal monitoring to echocardiography.

In contrast, NLFU delivers low-frequency (40 kHz), low-intensity (0.2 to 0.6 W/cm2) ultrasound energy to the wound bed with no thermal effect. With most ultrasound therapy, a gel serves as a conduit to deliver sound waves to tissues. However, NLFU uses a saline mist, which eliminates contact with tissue and thus is painless.

NLFU can be performed by nurses with special training. The patient usually undergoes the procedure at the bedside three to five times per week, with the machine preset to a certain number of minutes based on wound measurement (length × width). Typically, the course of therapy ends when the desired outcome is achieved or the patient is discharged or transferred out of the facility.

The science of NLFU

The micromechanical forces produced by ultrasound energy at a cellular and molecular level have a wide range of effects on the wound-healing process, including reduction of bacteria within and below the wound bed. Unlike other body cells, bacteria have a rigid cell membrane; repeated pressing of sound waves can disrupt the bacterial membrane, causing cell death. (See NLFU: The science behind the solution by clicking the PDF icon above.)

Laboratory tests show NLFU reduces a wide range of bacteria, including some of the hardest to treat, such as methicillin- resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), and Acinetobacter baumannii. In a clinical study of patients who had stage III pressure ulcers with high levels of bacteria, punch biopsies were used to determine baseline and posttreatment bacterial counts. Results showed significant reduction in S. aureus (93.9%), A. baumannii (94%), and Escherichia coli (100%) after six NLFU treatments over a 2-week period. In live animal studies, NLFU disrupted the bacterial biofilm after just three treatments. (See NLFU and the healing process by clicking the PDF icon above.)

Sustained inflammation is a common barrier to healing. NLFU reduced pro- inflammatory cytokines in two studies—one involving patients with chronic diabetic foot ulcers and the other involving patients with nonhealing venous leg ulcers. This reduction correlated to reduced wound areas in these previously nonhealing wounds. In one of these studies, researchers reported a decrease in MMP-9, a matrix metalloproteinase that breaks down new granulation tissue and delays healing.

Studies also show NLFU increases vasodilation, stimulates vascular endothelial growth factor and angiogenesis, promotes early release of growth factors, and provides greater amounts of high-quality collagen. The overall result of these cellular effects is accelerated healing.

Clinical outcomes

Use of NLFU is supported by clinical data, including a meta-analysis, three randomized-control trials, 11 peer-reviewed studies, and multiple case series. A 2011 meta-analysis compiled data from eight published studies reporting the effect of NLFU on wound size and healing rates in 444 patients with various chronic wounds. It found 85% wound-area reduction in a mean of 7 weeks, wound-volume reduction of 80% at a mean of 12 weeks, and 42% complete wound closure at 12 weeks. By comparison, a meta-analysis of standard-of-care treatment found only 24% complete wound closure at 12 weeks. Thus, NLFU achieves almost twice the healing of the standard treatment.

Besides consistently speeding healing of open wounds, NLFU is an effective early treatment for suspected deep-tissue injuries (sDTI). In a study of 127 sDTIs treated with standard of care alone (63) or standard of care with NLFU (64), only 22% of standard-of-care-alone sDTIs resolved without opening or progressed only to a stage II pressure ulcer, compared to 80% in the NLFU arm. At my hospital, we found similar results in our patient population using NLFU to resolve sDTIs before they became full-thickness wounds. (See Clinical outcomes and cost savings from NLFU by clicking the PDF icon above.)

NLFU has been used in wound care settings across the country for several years. Increasingly, it’s being used in acute-care settings as clinicians are grasping its substantial clinical and economic benefits. This technology can help healthcare providers meet both clinical and economic outcome goals. NLFU is rapidly becoming the new standard for early sDTI intervention.

Selected references

Centers for Medicare & Medicaid Services. Hospital-acquired conditions in acute inpatient prospective payment system hospitals. October 2012. www.cms.gov/ Medicare/Medicare-Fee-for-Service-Payment/Hospital AcqCond/downloads/hacfactsheet.pdf. Accessed July 13, 2013.

Driver VR, Yao M, Miller CJ. Noncontact low- frequency ultrasound therapy in the treatment of chronic wounds: a meta-analysis. Wound Rep Reg. 2011;19(4):475-80.

Escandon J, VIvas AC, Perez R, Kirsner R, Davis S. A prospective pilot study of MIST therapy’s effectiveness on bacterial bioburden reduction and wound progression in refractory venous leg ulcers. Poster presented at Symposium on Advanced Wound Care; Orlando, FL. April 17-20, 2010.

Honaker JS, Forston MR, Davis EA, Wiesner MM, Morgan JA. Effects of noncontact low-frequency ultrasound on healing of suspected deep tissue injury: a retrospective analysis. Int Wound J. 2013;10(1):65-72.

Kavros SJ, Miller JL, Hanna SW. Treatment of ischemic wounds with noncontact, low-frequency ultrasound: the Mayo Clinic experience, 2004-2006. Adv Skin Wound Care. 2007;20(4):221-6.

Kavros SJ, Schenck EC. Use of noncontact low-frequency ultrasound in the treatment of chronic foot and leg ulcerations: a 51-patienr analysis. J Am Podiatr Med Assoc. 2007;97(2):95-101.

Lai J, Pittelkow MR. Physiological effect of ultrasound mist on fibroblasts. Int J Dermatol. 2007;46(6):587-93.

Liedl DA, Kavros SJ. The effect of MIST ultra-sound transport technology on cutaneous microcirculatory blood flow. Abstract presented at Symposium on Advanced Wound Care, 2001.

Margolis DJ, Kantor J, Berlin JA. Healing of diabetic neuropathic foot ulcers receiving standard treatment. A meta-analysis. Diabetes Care. 1999;22(5):692-5.

Serena T, Lee SK, Lam K, Attar P, Meneses P, Ennis W. The impact of noncontact, nonthermal, low-frequency ultrasound on bacterial counts in experimental and chronic wounds. Ostomy Wound Manage. 2009;55(1):22-30.

Seth AK, Nguyen KT, Geringer MR, et al. Noncontact, low-frequency ultrasound as an effective therapy against Pseudomonas aeruginosa–infected biofilm wounds. Wound Repair Regen. 2013;21(2):266-74.

Thawer HA, Houghton PE. Effects of ultrasound delivered through a mist of saline to wounds in mice with diabetes mellitus. J Wound Care. 2004;13(5):171-6.

Yao M, Hasturk H, Kantarci A, et al. A pilot study evaluating noncontact low frequency ultrasound and underlying molecular mechanism on diabetic foot ulcers. Int Wound J. 2012 Nov 19. doi:10.1111/iwj.12005.

Ronnel Alumia is a wound care and ostomy nurse at Acuity Specialty Hospital of New Jersey in Atlantic City.